CHARACTERIZATION AND REGULATION OF INSULIN-LIKE-GROWTH-FACTOR BINDING-PROTEINS IN HUMAN HEPATIC STELLATE CELLS

Cultured hepatic stellate cells (HSCs), the cell type primarily involv ed in the progression of liver fibrosis, secrete insulin-like growth f actor-I (IGF-I) and IGF binding protein (IGFBP) activity. IGF-I exerts a mitogenic effect on HSCs, thus potentially contributing to the fibr ogenic process in an autocrine fashion, However, IGF-I action is modul ated by the presence of specific IGFBPs that may inhibit and/or enhanc e its biologic effects. Therefore, we examined IGFBP-1 through IGFBP-6 mRNA and protein expression in HSCs isolated from human liver and act ivated in culture. Regulation oi IGFBPs in response to IGF-I and other polypeptide growth factors involved in the hepatic fibrogenic process was also assessed. RNase protection assays and ligand blot analysis d emonstrated that HSCs express IGFBP-2 through IGFBP-6 mRNAs and releas e detectable levels of IGFBP-2 through IGFBP-5. Because IGF-I, platele t-derived growth factor-BB (PDGF-BB), and transforming growth factor-b eta (TGF-beta) stimulate HSC proliferation and/or matrix production, w e tested their effect on IGFBPs released HSCs. IGF-I induced IGFBP-3 a nd IGFBP-5 proteins in a time-dependent manner without an increase in the corresponding mRNAs. IGFBP-4 protein levels decreased in response to IGF-I. IGF-beta stimulated IGFBP-3 mRNA and protein but decreased I GFBP-5 mRNA and protein. In contrast, PDGF-BB failed to regulate IGFBP s compared with controls. Recombinant human IGFBP-3 (rhlGFBP-3) was th en tested for its effect on IGF-1-induced mitogenesis in HSCs. rhlGFBP -3 inhibited IGF-I-stimulated DNA synthesis in a dose-dependent manner , with a peak effect observed at 25 nM IGFBP-3. Because TGF-beta is hi ghly expressed in cirrhotic river tissue, we determined whether IGFBP- 3 mRNA expression is increased in liver biopsies obtained from patient s with an active fibroploliferative response due to viral-induced chro nic active hepatitis. In the majority of these samples, IGFBP-3 mRNA w as increased compared with normal controls. These findings indicate th at human HSCs, in their activated phenotype, constitutively produce IG FBPs. IGF-I and TGF-beta differentially regulate IGFBP-3, IGFBP-4, and IGFBP-5 expression, which, in turn, may modulate the in vitro and in vivo action of IGF-I. (C) 1998 Wiley-Liss, Inc.